1) Field of the Invention
The invention relates to a crosslinkable powder composition which is redispersible in water and also to its use.
2) Background Art
EP-A 601518 describes crosslinkable dispersion powders which are redispersible in water and based on carboxyl-containing acrylate copolymers which are dried in the presence of polyvinyl alcohol and can contain polyvalent metal ions for crosslinking. Similar crosslinkable dispersion powders are also known from U.S. Pat. No. 3,409,578 in which powder compositions comprising carboxyl-containing polymers and/or carboxyl-containing protective colloids are crosslinked in the presence of polyvalent metal ions. A disadvantage is that such compositions comprising polyvalent metal salts which liberate acid in the presence of water tend to crosslink prematurely, especially in contact with moisture.
To avoid premature crosslinking, EP-A 702059 (U.S. Pat. No. 5,608,011) proposes using crosslinkable dispersion powders comprising N-methylol-containing copolymers and a catalyst combination of water-soluble or water-dispersible peroxo acid salts or reducing agents. EP-B 687317 describes crosslinkable powders which are redispersible in water and are based on N-methylol-functional copolymers which crosslink on heating. A disadvantage of the latter powder is the fact that exclusively heat-crosslinkable powders cannot be used in many applications.
EP-A 723975 discloses crosslinkable dispersion powders based on copolymers containing epoxide groups. For crosslinking, external crosslinkers such as polyamines, polycarboxylic acids, hydroxy-functionalized polymers and polyvalent metal salts are added. A problem with the use of polyamines or polyvalent metal salts is the low storage stability.
EP-A 721004 discloses crosslinkable, redispersible powder mixtures comprising film-forming polymer particles having at least one functional, crosslinkable group. The crosslinker component can be a water-soluble or emulsifiable monomer or polymer, or else a pulverulent mixture of the crosslinker and an inorganic carrier such as CaCO.sub.3, clay or silicon dioxide. The crosslinker component is bound to these carrier substances by physical adsorption. This has the disadvantage that these mixtures have the same odor, if somewhat attenuated, as the pure crosslinker component. In addition, owing to the weak physical bonding, the crosslinker component can become detached and penetrate into the polymer to be crosslinked, which, particularly in the case of very reactive substances, can lead to a reduced shelf life or premature crosslinking.
It is therefore an object of the invention to provide a crosslinkable powder composition which is redispersible in water and has a high storage stability and blocking stability and is free-flowing.